1. Field of the Invention
This system described herein relates to data storage facilities and more specifically to the field of transferring the functionality of data storage facilities.
2. Description of Related Art
Host processor systems may store and retrieve data using a storage device containing a plurality of host interface units (host adapters), disk drives, and disk interface units (disk adapters). Such storage devices are provided, for example, by EMC Corporation of Hopkinton, Mass. and disclosed in U.S. Pat. No. 5,206,939 to Yanai et al., U.S. Pat. No. 5,778,394 to Galtzur et al., U.S. Pat. No. 5,845,147 to Vishlitzky et al., and U.S. Pat. No. 5,857,208 to Ofek. The host systems access the storage device through a plurality of channels provided therewith. Host systems provide data and access control information through the channels to the storage device and the storage device provides data to the host systems also through the channels. The host systems do not address the disk drives of the storage device directly, but rather, access what appears to the host systems as a plurality of logical disk units. The logical disk units may or may not correspond to the actual disk drives. Allowing multiple host systems to access the single storage device unit allows the host systems to share data stored therein.
In some instances, it may be desirable to copy data from one storage device to another. For example, if a host writes data to a first storage device, it may be desirable to copy that data to a second storage device provided in a different location so that if a disaster occurs that renders the first storage device inoperable, the host (or another host) may resume operation using the data of the second storage device. Such a capability is provided, for example, by the Remote Data Facility (RDF) product provided by EMC Corporation of Hopkinton, Mass. With RDF, a first storage device, denoted the “primary storage device” (or “R1”) is coupled to the host. One or more other storage devices, called “secondary storage devices” (or “R2”) receive copies of the data that is written to the primary storage device by the host. The host interacts directly with the primary storage device, but any data changes made to the primary storage device are automatically provided to the one or more secondary storage devices using RDF. The primary and secondary storage devices may be connected by a data link, such as an ESCON link, a Fibre Channel link, and/or a Gigabit Ethernet link. The RDF functionality may be facilitated with an RDF adapter (RA) provided at each of the storage devices.
RDF may be used to provide for disaster recovery, whereby one or more R2 devices are provided in remote site(s) along with remote host device(s). The R1 storage device(s) are provided at a primary site with one or more host(s) that perform the work for the system. When a failure occurs at a primary site, the work performed using the R1 device may be transparently shifted to the R2 storage device at a remote site. In such a case, the R2 device, which had been read only prior to the failure, becomes a writeable R2 device (and/or becomes an R1 device) that is usable by the host.
In some cases, the system may be designed/configured to rely on the R2 device(s) at remote site(s) being read only. For example, the data written at the primary site may be financial information that should only be writeable by a relatively secure host at the primary site even though it is readable by less secure host(s) at the remote site(s). After a failover occurs and the previously read only remote storage device(s) become writeable, it may be unacceptable to have the (less secure) remote host(s) be able to write data thereto. Note also that, even in instances where the remote host(s) do not actually write any data, the fact that the host(s) have write access may still be problematic (e.g., in situations where it is necessary to prove compliance to data handling regulations).
Accordingly, it is desirable to provide a system that addresses the issues set forth above.